Police are hunting a radical Muslim preacher wanted in connection with an acid attack on two British teenagers in Zanzibar.

Sheikh Issa Ponda Issa was cornered by officers near Dar es Salaam in Tanzania, but managed to escape and is now on the run.

He was hit in the shoulder with a tear-gas canister during the altercation, according to local police in Morogoro - the scene of the clash.

Police commander Faustine Shilogile said: "He has not been arrested. He has been shot at. We have been looking for him in all corners of the country."

He added: "We are no closer to finding who was responsible for this. But this is a serious police investigation, and we are doing everything we can."

Five men are also being questioned by officers, according to the authorities.

Image Caption:Kirstie Trup (L) and Katie Gee are being treated in London

News of the preacher's escape came as it emerged that one of the two men involved in the unprovoked attack "smiled" before throwing acid.

Speaking from Zanzibar, medical student Olivia Moore told Channel 4 News: "The two men were on a moped and they went past a group of tourists.

"They stopped for the girls and the two men then looked at each other, nodded and then the man on the back of the bike smiled and threw acid on the girls.

"From then on it's just chaotic. There was no incident that preceded the actual attack.

"Everyone was shocked. Nobody can think of a motivation or anything that precipitated this."

Victims Katie Gee, and Kirstie Trup, both 18 and from London, are still being treated for burns at Chelsea and Westminster Hospital after arriving home on Friday.

They are said to be "well rested and comfortable".

Image Caption:The street on the island where the attack took place

A hospital spokesman said: "They have been with their families all day. Doctors are continuing to assess treatment options for both patients."

The pair were attacked as they walked across a road on Wednesday night.

They had been nearing the end of a trip working as volunteer teachers on Zanzibar, a predominantly Muslim island in the Indian Ocean.

Witnesses have spoken of their desperate attempts to wash the acid off the two girls before they were rushed to hospital.

A picture released by the teenagers' families shows one appears to have extensive acid burns on her chin, neck and upper chest.

It is thought one of the girls is not as badly injured as the other because she was helped into the sea immediately after the attack.

They had apparently been due to return to the UK to collect their A-level results next week.

Miss Trup is hoping to study history at the University of Bristol and Miss Gee is considering the University of Leeds, according to reports.

Meanwhile, Tory MP Bill Cash, who sits on the all-party parliamentary group for Tanzania, has urged the Foreign Office to further upgrade its travel warning for tourists visiting both Zanzibar and Tanzania because it was "more than just an ordinary criminal event".

The Foreign Office updated its Tanzania travel advice page on Friday with details of the attack and warns British nationals to "take care" and read its travel advice.

Mr Cash said: "People need to be extra vigilant and the Foreign Office and High Commission need to make a very thorough evaluation of the threat, as these latest attacks would seem to be on religious grounds.

"The threat to tourists going to Tanzania and Zanzibar needs to be upgraded without doubt."